Conventionally, when clean water is heated to supply hot water, clean water is allowed to flow into a hot water supply apparatus from an entrance water side thereof, and heat of the clean water is exchanged directly for heat generated from a heat source such as a burner.
Concerning such a hot water supply apparatus, it is known that water is supplied to a heat exchanger disposed inside a water boiler, and combustion heat of a gas burner is exchanged for the water to provide hot water from an outgoing hot water pipe (for example, Japanese Laid-open Patent Publication No. 58-33050). It is also known that heat of clean water, which is supplied tap water processed by a water purifier, creating equipment that electrolyzes tap water to be able to generate alkaline water and acid water, etc., is exchanged for heat of a burner in a heat receiving pipe (for example, Japanese Laid-open Utility Model Publication No. 05-02619).
There is a case that tap water or the like taken into a hot water supply apparatus as clean water includes different components according to, for example, an area. If this difference is explained by a pH (Potential of Hydrogen) level, there exists the range of, for example, 5.8 to 8.6. When a pH level is very low, an acid level is high. Water of the very low pH level is not suitable to drink. When a pH level is high, an alkali level is high, and there may be a case that much lime is included as a component. If water of such high alkali level continues on being heated at high temperatures by a heat exchanger, there occurs possibility that the component of lime separates out in a heat exchanger. If a gap is generated between such separating component and a straight pipe of a heat exchanger, partial boiling may occur. Thus, there is a problem such that hot water at a desired temperature cannot be obtained.
Since a process such as filtration is executed on tap water in a water purification plant, impurities, etc. as the above do not multiply sharply. However, quality of supplied water is different according to an area because of difference in water quality before the process or in ability to purify water. For evening up water quality and supplying constant quality of water to a hot water supply apparatus, there are the problems of needing complicated devices and great cost.
Concerning such problems, there is no disclosure or suggestion thereof in Japanese Laid-open Patent Publication No. 58-33050 and Japanese Laid-open Utility Model Publication No. 05-026191, and no disclosure or suggestion about structure, etc. solving them are presented therein.